Filter device for filtering fibers from a flow and method for its operation

Abstract

A filter device (10) for filtering fibers from a flow for a feed device (20) for feeding the fibers in the production of fiber-reinforced plastics has at least one filter plate (52) which can be arranged in a housing recess (74) connected to a housing bore (76) of the feed device (20) and has a curvature (90) corresponding to the shape of the at least one housing bore (76). The filter plate (52) has at least one region (64) with several slit-shaped flow channels (58). At a predetermined flow rate in a flow direction (110) and at a Reynolds number below a critical Reynolds number, the flow channels generate laminar flows in the flow channels (58). These generate a homogeneous and uniform pressure distribution in the region (64) of the at least one filter plate (52). A method for operating the filter device (10) generates the flows accordingly.

Description

Field of invention

[0001] The present invention relates to a filter device for filtering fibers from a flow, which is configured for feeding the fibers in the production of fiber-reinforced plastics, having the features according to the preamble of claim 1, a corresponding feeding device for feeding fibers with a filter device having the features according to the preamble of claim 16 and a method for operating a filter device for filtering fibers from a flow for such a feeding device having the features according to the preamble of claim 17. State of the art

[0002] In the production of fiber-reinforced plastics, fibers such as glass fibers, carbon fibers, or fibers from renewable resources are incorporated into the plastics to increase their strength and stability. For this purpose, bundles of fibers are fanned out and cut into fiber pieces of the desired length in a shredding device. These pieces are then transported by a feeding device, such as a screw extruder, to a unit where raw materials, such as plastic granules, are plasticized. In this plasticizing unit, the molten plastics are mixed with the fiber pieces.

[0003] Such a feeding device typically consists of a screw conveyor through which the fiber pieces are transported towards the plasticizing unit. During the comminution of the fibers, waste products such as fiber dust or very short fiber fragments are generated. Both the fiber pieces and the waste products are drawn into the screw conveyor by the comminution device via a flow, such as an airflow, generated by a suction device. The fiber pieces are also drawn to the underside of the screw conveyor, or the side opposite the fiber feed point, thereby achieving a uniform distribution within a housing bore of the screw conveyor, particularly around the at least one conveying element located therein. The waste products, on the other hand, are removed from the airflow in the housing bore by a filter device located between the housing bore and the suction device.A disadvantage of the current state of the art is that the waste products lead to a blockage of the filter system after a relatively short time, resulting in increased maintenance requirements.

[0004] Previous solutions for filter systems use, for example, filter fleeces with fine-mesh filter structures, filters with perforations, or filters with filter lamellae.

[0005] EP 2 218 568 A1 discloses a screw machine for processing at least partially powdered bulk material, comprising a housing with at least one housing bore and a screw arranged in the housing bore. A vacuum housing section is provided, designed as a detachably mounted vacuum housing insert in which a metal fleece is held replaceably as a gas-permeable wall section on a base body.

[0006] WO 2014 / 048667 A1 discloses a feeding device for fibers using a multi-screw machine for the lateral feeding of fibers into a processing plant for the production of fiber-reinforced plastics. The multi-screw machine comprises a housing, several intersecting housing bores, rotatably driven screw shafts arranged therein, and a feed opening. A suction device is provided for drawing the fibers through the feed opening into the housing bores, generating an airflow that draws the fibers in. The fibers are filtered out of the airflow by means of a filter device. To ensure a long service life, the filter device has several flow channels with a cross-section that widens abruptly in one direction of flow.

[0007] The filter assembly of WO 2014 / 048667 A1 consists of a series of interconnected metallic lamellae, between which flow channels form. These channels abruptly widen in cross-section and, in particular, in width in the direction of flow towards the underside of the filter assembly. This abrupt change affects the flow parameters, leading to vortex formation, turbulence, backflow at the separation point / area, and sudden pressure changes. The effect is comparable to flow resistance. Due to the inconsistent cross-sections, inconsistent pressure conditions or pressure differences arise within the flow channels. These promote fiber accumulation and clogging of the filter assembly.The special geometry of the filter pack, constructed from lamellae, with its inconsistent cross-sections in the flow direction and inconsistent pressure conditions, promotes a fanning effect, where the lamellae open or spread apart, leading to fiber accumulation and clogging. To counteract this, a high tightening torque is used during lamella assembly, which can, conversely, cause distortion or deflection of the lamellae, resulting in inconsistent cross-sections between them. During assembly, especially after filter maintenance, contamination can occur in the flow channels and between the contact surfaces of the spacer plates between the lamellae, leading to assembly inaccuracies. These inaccuracies accumulate with each additional spacer plate.All of this can lead to unfavorable flow conditions. Similarly, assembly errors in the orientation of the individual lamellae can result in problematic flow patterns. Ultimately, all these problems can lead to fluctuations in the fiber content of fiber-reinforced plastics, preventing compliance with customer-required quality criteria. Finally, the geometry of the lamellae defines the installation position of the filter assembly, precluding any other arrangement, such as rotation. Description of the invention

[0008] The invention is therefore based on the objective of providing a filter device that increases the reliability of the filter process and the quality of the fiber-reinforced plastics produced.

[0009] This problem is solved by a filter device according to the features of claim 1. The filter device comprises, as a filter element, at least one filter plate with a curvature, wherein the filter plate has at least one region with several slit-shaped flow channels which, in the operating state at a predetermined or predeterminable flow rate, have a Reynolds number below a critical Reynolds number above which the flow becomes turbulent, and are thus configured to form a laminar flow in the flow channels and a homogeneous and uniform pressure distribution in the region.

[0010] The laminar flow in the flow channels advantageously leads to a homogeneous pressure distribution on the upper and lower surfaces of the at least one filter plate. This effectively slows down or ideally prevents the accumulation of waste products, such as fiber dust or short fiber fragments, in the filter system and thus clogging of the filter system. Furthermore, this improves the quality of the fiber-reinforced plastics produced, as a constant amount of fiber can be introduced into the plasticization process, resulting in a precise, preferably consistent, desired fiber content in the fiber-reinforced plastic.Furthermore, this enables a reduction in the number of parts in the filter system, reduces the susceptibility to errors during filter assembly, simplifies assembly and maintenance, reduces cleaning time during preventive cleaning of the filter system, and thus achieves increased machine availability while simultaneously reducing costs.

[0011] The problem is also solved with a feeding device for supplying fibers during the production of fiber-reinforced plastics, comprising a filter device according to the features of claim 16. The feeding device further comprises a filter device according to any one of claims 1 to 15. This provides the advantages of the invention.

[0012] Furthermore, the problem is also solved by a method for operating a filter device for filtering fibers from a flow, such as an airflow, used to supply the fibers during the production of fiber-reinforced plastics, according to the features of claim 17. The filter device comprises, as a filter element, at least one filter plate with a curvature, which filter plate has at least one area with several slit-shaped flow channels. In the operating state, at a predetermined or predeterminable flow rate and a Reynolds number below a critical value, these channels generate laminar flow and a homogeneous and uniform pressure distribution. The advantages of the invention are thereby realized.

[0013] Beneficial further training is subject to dependent claims.

[0014] In a preferred embodiment of the filter device, the stability of the filter device is advantageously increased and maintenance simplified by the fact that the filter plate has a closed comb and that the slit-shaped flow channels are several parallel, slit-shaped flow channels, each with a constant flow cross-section and a predetermined length-to-width ratio. The closed comb increases the stability of the filter plate, which in turn also contributes to stable laminar flow. Likewise, the consistently uniform cross-sections or gap dimensions of the flow channels contribute to maintaining laminar flow.

[0015] Preferably, in one embodiment of the filter device, the wall accommodating the filter plate is a cylindrical wall with an inner radius to accommodate a conveying element with a cylindrical cross-section, such as a screw shaft of a feeding device for supplying the fibers to a processing plant. The wall is designed to be swept by the conveying element, arranged in at least one bore of the housing, preferably without contact, as the filtered fibers are transported away. The filter element is pre-curved and has a curvature along the bore of the housing corresponding to its shape. This advantageously allows the filtered fibers to be reliably fed to the processing plant. At the same time, the conveying element regularly exposes the filter plate to maintain its filtering effect.

[0016] In another embodiment of the filter device, the radius of curvature of the filter plate in its uninstalled state is larger than the inner radius of the wall. This allows the filter plate to be advantageously clamped and fixed to the wall using appropriate fixing elements such as grooves.

[0017] Preferably, the filter assembly has a frame or a receptacle with at least one curvature corresponding to the curvature of the wall, on which the at least one filter plate is replaceably mounted, wherein, in the operating state, the frame is preferably arranged in a housing recess connected to the at least one housing bore. This advantageously increases the stability of the filter assembly and simplifies maintenance.

[0018] Preferably, a stable fixation of the at least one filter plate and easy replacement or rotation of the at least one filter plate can be advantageously facilitated in a further embodiment of the filter device, taking into account the leaf-spring-like properties of the at least one filter plate, which is pre-tensioned with its outer edges, which preferably run along a longer side of the filter plate, positively and / or frictionally locked, preferably both positively and frictionally locked, in grooves of the frame or the receptacle. With the filter plate fixed in this way, replacement or rotation of the at least one filter plate about an axis transverse to its surface area can thus be carried out without tools and with comparatively little effort.

[0019] Advantageous for the efficiency of the feeding device and a more uniform distribution of the fibers in the plastic, in another preferred embodiment the filter device can have several adjacent filter plates with bulges, which are mounted on several corresponding bulges of the frame or the receptacle and which, in the operating state when using a multi-shaft screw machine with several adjacent, intersecting housing bores of the housing with a screw shaft arranged therein, can be arranged in a housing recess connected to the housing bores.The frame between the filter plates has at least one central web with grooves into which an outer edge of one of the several adjacent filter plates, which preferably runs along a longer side of the filter plate, is received in a form-fitting and / or force-fitting manner, preferably both form-fitting and force-fitting manner.

[0020] In a further preferred embodiment, replacing or rotating the at least one filter plate can be advantageously accomplished simply by the fact that the at least one filter plate has symmetrical properties and is designed to allow installation in the frame or receptacle rotated by 180°, and that the frame and the at least one filter plate are designed to allow replacement or rotation of the at least one filter plate by means of a sliding removal of the at least one filter plate from the grooves of the frame. Due to the symmetry properties of the filter plates, their service life can advantageously be extended by rotating the filter plates by 180°.

[0021] Preferably, the filter assembly has symmetrical properties and can therefore be installed in the housing recess rotated by 180°. Due to the symmetry of the mounted filter assembly, a rotation of the entire filter assembly by 180° is also possible. This advantageously prevents assembly errors from the outset and increases the service life of the filter assembly.

[0022] A preferred embodiment of the filter device enables both a particularly stable fixing of the at least one filter plate and a simple replacement or rotation of the at least one filter plate, advantageously in that the at least one filter plate is detachably fastened to the frame or the receptacle with two locking plates arranged at the end face of the frame, preferably by means of screws, and secured against displacement in the grooves.

[0023] In a preferred embodiment, the stability of the at least one filter plate with respect to its vibration behavior and its deflection strength can preferably be advantageously improved by the at least one filter plate having several separate areas with several slit-shaped flow channels extending transversely to the at least one housing bore, preferably along a longer side of the filter plate.

[0024] Another preferred embodiment of the filter device or the method for operating a filter device enables particularly good results with regard to maintenance behavior, advantageously by designing the flow channels to generate a pressure drop in an optimal range of around 50 mbar. Tests have shown that at pressure drops of this value, clogging can be efficiently reduced or prevented. If the pressure drop becomes too large for a given gap width, the flow enters the turbulent range.

[0025] Preferably, the vibration behavior and the deflection strength of the at least one filter plate and the quality of the laminar flow in the flow channels are advantageously improved by the fact that the at least one filter plate has a thickness between 0.5mm and 2mm.

[0026] In a preferred embodiment, the frame or receptacle downstream of and following the filter plate has at least one chamber with a cross-section that remains constant in the flow direction. This allows the pressure conditions downstream of the filter plate to remain nearly constant, which advantageously contributes to maintaining laminar flow.

[0027] Preferably, in another embodiment, the effectiveness of the filter device can be further improved by arranging the frame or the receptacle in the housing recess in a substantially airtight or flow-tight manner. When using a frame instead of a fixed installation or integration of the at least one filter plate into the housing recess, a substantially airtight connection of the frame in the housing recess prevents the formation of undesirable turbulence in the filter device.

[0028] A preferred embodiment of the method for operating a filter device enables secure fixing of the at least one filter plate and yet allows for easy replacement or...A simple rotation of the at least one filter plate is advantageous in that the filter device has a frame or a receptacle on which the at least one filter plate is interchangeably mounted, wherein the frame has at least one curvature corresponding to the curvature of the at least one filter plate on which the at least one filter plate is mounted, that the at least one filter plate has leaf spring-like properties and is pre-tensioned with its outer edges, which run along a preferably longer side of the filter plate, positively and / or force-fit, preferably both positively and force-fit, and that the at least one filter plate can be replaced without tools by sliding it in the grooves of the frame by means of another filter plate identical to the at least one filter plate, which engages the at least one filter plate on a preferably shorter side.

[0029] In another preferred embodiment of the method, electrostatic charging of the fibers used is advantageously prevented by using an ionized airflow. This particularly prevents the fibers from adhering to parts of the feeding device.

[0030] The features listed individually in the patent claims can be combined in a technologically meaningful way and can be supplemented by explanatory facts from the description and by details from the figures, showing further embodiment variants of the invention.

[0031] The invention will now be explained in more detail using an exemplary embodiment. The figures shown are: Fig. 1. A perspective view of a processing plant for the production of fiber-reinforced plastics, Fig. 2 a perspective sectional view of a feeding device, Fig. 3 a detailed view of the Fig. 2, Fig. 4 a perspective view of a filter device, Fig. 5 a perspective view of a frame, Fig. 6 a perspective exploded view of the Fig. 4, Fig. 7 a perspective view of a filter plate, Fig. 8 a perspective view of a filter plate replacement process, Fig. 9 a sectional view of a filter plate replacement process in operational condition, Fig. 10 a diagram that relates the pressure drop in the flow channels to the width of the flow channels, Fig. 11 a diagram that relates the Reynolds number of the flow in the flow channels to the width of the flow channels. Description of preferred embodiments

[0032] Before the invention is described in detail, it should be noted that it is not limited to the respective components of the device or the respective process steps, as these components and processes can vary. The terms used here are intended solely to describe particular embodiments and are not used restrictively. Furthermore, where the singular or indefinite articles are used in the description or in the claims, this also refers to the plural of these elements, unless the overall context clearly indicates otherwise.

[0033] Fig. Figure 1 shows a perspective view of a processing plant 40 for the production of fiber-reinforced plastics. This plant has a feeding device 20 for feeding fibers, such as glass fibers, carbon fibers or fibers made from renewable raw materials.

[0034] In the exemplary embodiment, according to Fig. 1 to an injection molding unit 160 on an injection molding machine for processing plastics and other plasticizable materials with a machine stand 150, of which only the injection molding side is visible.

[0035] The design and operation of an injection molding machine are generally known to those skilled in the art. Plastics or other plasticizable materials are fed into the injection molding machine and are plasticized in a 175 mm plasticizing cylinder. Fig. 2) are mixed, plasticized and homogenized in a plasticizing device 170 incorporated in the injection molding unit 160.

[0036] During the plasticizing process, plasticized material is metered in front of a conveying device 190, such as a screw conveyor. Subsequently, the plasticized material is injected into a mold cavity of an injection mold (not shown in the drawing) by an axial movement of the conveying device 190. In the operating state, the mold mold is held between the mold carriers of the mold clamping unit. Of these mold carriers, only the stationary mold carrier 140 is visible in the figures, on which the Fig. The rest of the mold clamping unit would connect to the right side. During the injection process, the injection mold is closed by the mold clamping unit. Once the injected plasticized material has hardened in the mold cavity, the mold clamping unit opens the injection mold again so that the finished part can be removed. This process is repeated cyclically.

[0037] Fig. Figure 2 shows a perspective sectional view of the feeding device 20, by means of which fibers are added to the material. Fig. 3 shows a detailed view of the Fig. 2. The figure shows a fiber comminution device 100, which first fans out a bundle of fibers and then cuts them to a desired length. In the exemplary embodiment, the fiber comminution device 100 is arranged above a feeding device 20. The feeding device 20 comprises a screw conveyor 30 for the lateral feeding of fibers into the processing plant 40 for the production of fiber-reinforced plastics. The screw conveyor 30 has a housing 70 with at least one housing bore 76, at least one screw shaft 80 arranged concentrically in the at least one housing bore 76 and driven about an associated axis of rotation, and a feed opening 72 for feeding the fibers into the at least one housing bore 76.

[0038] The feeding device 20 also includes a suction device (not shown) for drawing the cut fibers through the feeding opening 72 into the at least one housing bore 76 by means of a flow, such as an airflow, with a predetermined or predeterminable flow rate or air delivery rate. A filter device 10 with at least one filter element arranged in and transverse to the flow in a wall 51 for filtering fibers from the flow can be arranged for the feeding device 20 between the suction device and the at least one housing bore 76. Alternatively or additionally to the suction device, a blowing device can also be provided.

[0039] The flow is usually an airflow or another gaseous flow, which may also contain air. In principle, however, any fluid capable of flowing can be used to generate the flow.

[0040] The filter device 10 has at least one filter plate 52 as a filter element, as shown in Fig. Figure 7 shows that, in the operating state, the filter plate is preferably arranged in a housing recess 74 connected to the at least one housing bore 76 and preferably has a curvature 90 corresponding to the shape of the at least one housing bore 76. The filter plate is a planar element, the surface having any shape, including three-dimensional shapes, here in the shape of the curvature 90.

[0041] The at least one filter plate 52 with a curvature 90 has at least one, in the exemplary embodiment substantially rectangular, region 64 with several parallel, slit-shaped flow channels 58 extending transversely to the at least one housing bore 76. In principle, the region can also have any other shape. Instead of rectangular, it can, for example, be round, oval, or even polygonal. Likewise, the slit-shaped flow channels 58 do not have to be arranged parallel to each other, provided that a suitable geometry ensures laminar flow through the filter plate 52. For example, concentric slit-shaped and / or annular or partially annular flow channels are also conceivable. In principle, the filter plate 52 does not have to have symmetrical properties, even though symmetry can offer advantages during maintenance and replacement of the filter plate.

[0042] The at least one flow channel 58 exhibits, in the operating state at a predetermined or predeterminable flow rate, a Reynolds number Re with a value below a critical Reynolds number Re krit on and is thus designed to form a laminar flow in and preferably before and after the flow channel 58 and a homogeneous and uniform pressure distribution in the area 64.

[0043] Preferably, the filter plate 52 is designed with a closed comb 53 to increase its stability, wherein the slit-shaped flow channels 58 included therein each have a constant flow cross-section and a predetermined ratio of length l to width b in order to influence the Reynolds number Re.

[0044] The wall 51, in which the filter plate 52 or filter device 10 is arranged, is preferably a cylindrical wall with an inner radius of a cylinder for receiving a conveying element with a cylindrical cross-section, such as the screw shaft 80. It is designed and arranged so that it, and thus the filter element arranged within it, is preferably swept over by the conveying element without contact during the removal of the filtered fibers. To accommodate the filter element in the wall 51, the filter plate 52 is pre-curved accordingly. Preferably, the radius of the curvature 90 of the filter plate 52 in its uninstalled state is larger than the inner radius of the wall 51.

[0045] The flow channels have the effect of several parallel Venturi nozzles. Preferably, in the operating state, at a predetermined or predeterminable flow rate in a flow direction 110 and at a resulting Reynolds number Re with a value below a predetermined critical range of the Reynolds number, in which the flow can become turbulent, they generate a pressure drop Δp in a predetermined range. This results in laminar flows in the flow channels 58, which generate a homogeneous and uniform pressure distribution in the at least one area 64 of the at least one filter plate 52, which is designed as a closed comb 53.

[0046] Before discussing the invention in more detail, the physical relationship between the Reynolds number Re of the flow channels 58 and the gap width of the flow channels 58 of the filter device according to the invention will first be explained.

[0047] The pressure drop Δp in a flow channel is proportional to the volume flow rate V̇ squared, with the flow resistance R as the proportionality factor: Δp=R⋅V˙2

[0048] The pressure drop Δp can also be defined via the resistance coefficient ζ: Δp=ζρ2v2, with ζ=const.

[0049] Substituting expression (2) into (1) yields the flow resistance R: R⋅V˙2=ζ⋅ρ2⋅v2 and with V˙=v⋅AR=ζ⋅ρ2A2

[0050] The total flow resistance value R Ges is less than the parallel individual resistances R S The total resistance decreases with each additional flow channel. At a constant volume flow rate V̇, the pressure drop Δp at the filter device is reduced (see equation (1)).

[0051] The total flow resistance value R Ges is calculated from the individual resistance values ​​R Saccording to the following relationship, where x and n represent the number of columns: Rtotal = 1(x⋅n1RS)2 = RS(x⋅n)2

[0052] The homogeneous, uniform pressure distribution in area 64 leads to the following approach: ΔpS=ΔpGes with (1) it follows RS⋅V˙S2=RGes⋅V˙Ges2 , cf. (3) at ζ=const.

[0053] From this, it follows with (4): RS⋅V˙S2=1(x⋅n1RS)2⋅V˙Ges2 or RS⋅V˙S2=RS⋅1(x⋅n)2⋅V˙Ges2

[0054] From (5) the relationship of the volume flow follows, in accordance with the continuity equation (6): V˙S=V˙Gesx⋅n

[0055] The continuity equation is used for an incompressible flow: V˙=const.

[0056] At the flow velocity v S at the gap: vS=V˙SAS=V˙GesAGes=V˙Suction deviceAGes

[0057] From (2) the continuity equation (6) is used to calculate the slit width b: Δp=ζ⋅ρ2⋅vS2→Δp=ζ⋅ρ2(V˙Gesx⋅n⋅AS)2→Δp=ζ⋅ρ 2(V˙Gesx⋅n⋅l⋅b)2→b=ζ⋅ρ⋅V˙Ges22Δp(x⋅n⋅l)2

[0058] To establish a relationship between the gap width b and the flow behavior, the Reynolds number Re is used as a key figure: Re=vs⋅dhv=ρ⋅vs⋅dhη.

[0059] With the hydraulic diameter d h as characteristic length: dh=4AsUs=4⋅l⋅b2⋅(l+b), where: Re~vs~V˙s and V˙s~V˙Ges→vs=V˙GesAGes=V˙Gesx⋅n⋅l⋅b

[0060] From (8), (9) and (10) the Reynolds number is: Re=ρη⋅V˙Tot(x⋅n⋅l⋅b)⋅4⋅l⋅b2(l+b)=2ρ⋅V˙Totη⋅x⋅n(l+b)

[0061] Solving for the total volume flow rate yields: V˙Tot=Re⋅η⋅x⋅n(l+b)2ρ.

[0062] Substituting the total volume flow rate from (12) into the equation (7) for the width yields the following relationship for the width of the flow channels: b=Re⋅η⋅lζl8⋅ρ⋅Δp−Re⋅ηζ→b=11Re⋅η⋅8⋅ρ⋅Δpζ−1l

[0063] The symbols in the formula have the following meaning: A Flow cross-sectional area b Width of the flow channel d h characteristic length, hydraulic diameter l Length of the flow channel Number of flow channels: 58 of the essentially rectangular area 64 Δp pressure drop R flow resistance Re Reynolds number U-shaped circumference wetted with fluid v speed V̇ Volume flow x Number of essentially rectangular areas 64 ζ Pressure loss coefficient, resistance coefficient η dynamic viscosity v kinematic viscosity ρ density

[0064] The following indices are sometimes used for the formula symbols: S Flow channel Total sum of all flow channels

[0065] In summary, the key formulas are: b=11Re⋅η8⋅ρ⋅Δpζ−1l Re=2ρ⋅V˙Totη⋅x⋅n(l+b) b=ζ⋅ρ⋅V˙Tot22 Δp(x⋅n⋅l)2

[0066] This leads to the following conclusions: • When the flow rate V̇ is increased Ges (Suction capacity) and thus an increase in Re, the pressure drop Δp increases with the same filter plate 52, i.e. with the same flow channel width b. [see: (11), (13)] • Conversely, if the same optimal pressure drop Δp at the filter plate 52 is to be achieved, then an increase in the extraction capacity V̇ must be achieved. Ges(by control, software) and thus the Reynolds number Re a different filter plate 52 with an increased flow channel width b is used. [see: (13)] • Another way to operate with a constant pressure drop Δp at the filter plate 52 at optimum would be to keep the Reynolds number Re constant by using a filter plate 52 with a higher number n of flow channels. [see: (11)] • To increase the pressure drop Δp across the filter plate 52, a filter plate 52 with a reduced flow channel width b is required at a constant Reynolds number Re. [see (13)] • Note: The Reynolds number Re represents the velocity v s and therefore also the volume flow rate V̇ Ges included. About the hydraulic diameter d hThe flow channel width b is also included, with minimal effect due to the large ratio of flow channel length l to flow channel width b. [see (11)]

[0067] The inventive effect of the at least one filter plate 52 is achieved by a constant flow cross-section of the flow channels 58 with a predetermined, in particular large, ratio of length l to width b, which generate the effect of several parallel Venturi nozzles. With a predetermined, i.e., constant, flow rate and the predetermined width b, a Reynolds number Re is achieved as a parameter that generates an optimal pressure drop Δp.

[0068] The curved line in Fig. Figure 10 represents a Reynolds number Re as a parameter in a diagram that indicates the dependence of a pressure drop Δp on a width b of the flow channels. To the left of the curve is a region 125 with laminar flow, and to the right is a region 126 with turbulent flow. In the laminar region 125, a minimum ("min.") and a maximum ("max.") possible value for the pressure drop Δp are shown, at which a filter device according to the invention operates substantially reliably. Also shown is an optimal region of pressure drop Δp, located between the marks marked "opt." The filter device according to the invention operates most effectively in this region.

[0069] In Fig. Figure 11 illustrates the relationship between the width b of the flow channels and a Reynolds number Re, using various values ​​of a pressure drop Δp as a parameter. The reference number 120 refers to a pressure drop above a critical Reynolds number Re. krit lying area in which a turbulent flow would occur and a filter device according to the invention would no longer function, wherein the reference numeral 121 indicates the maximum value of a Reynolds number Re that is still permissible.

[0070] Reference numeral 122 denotes a minimum possible pressure drop Δp, and reference numeral 124 a maximum possible pressure drop Δp at which the filter device 10 still operates reliably. Reference numeral 123 denotes an optimal pressure drop Δp, preferably around 50 mbar, at which the filter device 10 operates most effectively. Values ​​between the minimum and maximum possible pressure drops, ideally within the optimal range, ensure that the Reynolds number Re remains within a range where laminar flow is maintained. Conversely, if the pressure drop becomes too large for a given gap width, the flow enters the turbulent range.

[0071] It is advantageous for increasing the stability of the filter assembly 10 and simplifying maintenance if the filter assembly 10 has a frame 50 or a receptacle, as exemplified in Fig. Figure 5 shows a frame on which at least one filter plate 52 is mounted in an exchangeable manner, the frame 50 having at least one curvature 90 corresponding to the curvature 90 of the at least one filter plate 52, on which the at least one filter plate 52 is mounted. The frame 50 can be designed such that either only one or more filter plates 52 can be accommodated.

[0072] The terms frame and mount are generally used synonymously and without restriction. They are suitable for holding the filter plates 52 in the filter assembly 10. In the following, the term "frame" will be used in this sense.

[0073] A stable fixing of the at least one filter plate 52 and a simple exchange or rotation of the at least one filter plate 52 can be easily made possible by the fact that the at least one filter plate 52 has leaf spring-like properties and is pre-tensioned with its outer edges, which preferably run along a longer side 66 of the filter plate 52, but can also run along a shorter side, being received in grooves 62 of the frame in a form-fitting and force-fitting manner.

[0074] For the efficiency of the feeding device 20 and a more uniform distribution of the fibers in the plastic, it is advantageous if the filter device 10 has several adjacent filter plates 52 with bulges 90, which are mounted on several corresponding bulges 90 of the frame. In the operating state, when using a multi-shaft screw machine 30 with several adjacent, intersecting housing bores 76 of the housing 70, each with a screw shaft 80 arranged therein, these can be arranged in a housing recess 74 connected to the housing bores 76.In this case, the frame 50 has at least one central web 60 with grooves 62 between the filter plates 52, into which an outer edge 66 of one of the several adjacent filter plates 52, which runs along a preferably longer side 66 of the filter plate 52, is engaged in a form-fit and / or force-fit manner, preferably both form-fit and force-fit. This is illustrated by example in . Fig. 4 and Fig. 5 shown.

[0075] Replacing or rotating the at least one filter plate 52 is easily accomplished because the at least one filter plate 52 has symmetrical properties and is designed to allow installation in the frame 50 rotated by 180°. The frame 50 and the at least one filter plate 52 are designed to allow replacement or rotation of the at least one filter plate 52 by means of a sliding removal of the at least one filter plate 52 from the grooves 62 of the frame 50. This reversal increases the service life of the filter plate 52. While in the prior art, the orientation during installation is relevant for filter packages consisting of spacer plates / lamellae due to the one-sided cross-sectional change in the flow channel, the design of the filter plate 52 and its mounting now ensures reliable installation.

[0076] The symmetry of the mounted filter assembly 10 also allows for a 180° rotation of the filter assembly. This simultaneously prevents errors during assembly (Poka-Yoke, meaning "avoiding unfortunate errors," refers to a multi-element principle that includes technical precautions or devices for the immediate detection and prevention of errors). While in the prior art, the orientation during installation of the filter assembly consisting of spacer plates / lamellae is relevant due to the one-sided cross-sectional change in the flow channel, the design of the filter plate 52 and its bearing now ensures error-free installation reliability.

[0077] A particularly stable fixing of the at least one filter plate 52 and a simple exchange or rotation of the at least one filter plate 52 can be equally advantageous as in Fig. 6 shown, this enables the at least one filter plate 52 on the frame 50 to be secured against displacement in the grooves 62 by two locking plates 54, which are arranged at the front of the frame 50 and are preferably detachably attached to it by means of screws 56.

[0078] The stability of the at least one filter plate 52 with respect to its vibration behavior and its deflection strength can be improved by the fact that the at least one filter plate 52 preferably has several, in the exemplary embodiment two, e.g. essentially rectangular, separated areas 64 with several slit-shaped flow channels 58 extending transversely to the at least one housing bore along a longer side of the filter plate 52. This is exemplified in Fig. Figure 7 shows that the at least one filter plate 52 can be arranged between the essentially rectangular, separated areas 64 on at least one crossbar 92 of the frame 50, which supports the at least one filter plate. This gives the at least one filter plate 52 additional stability. Fig. 5 and Fig. Figure 6 shows the crossbars 92.

[0079] In one embodiment of the filter device 10 or of the method for operating a filter device 10, particularly good results with regard to maintenance behavior can be achieved by designing the flow channels 58 to generate a pressure drop Δp in the range of approximately 50 mbar. This corresponds approximately to the optimal range (line 123) in Fig. 11. Values ​​up to the minimum values ​​(line 122) and maximum values ​​(line 124) specified there are still possible. This effectively prevents clogging of the filter unit 10. However, if this range is exceeded, for example, if the pressure drop becomes too large for a given gap width, the system enters the turbulent range, which promotes fiber accumulation and clogging.

[0080] The vibration behavior and the deflection strength of the at least one filter plate 52 and the quality of the laminar flow in the flow channels 58 can be improved by the at least one filter plate 52 having a thickness between 0.5mm and 2mm.

[0081] Preferably the frame 50 is located downstream of the filter plate 52 in the direction of flow and following the filter plate according to Fig. 5 is designed such that it has at least one chamber 49 with a cross-section that preferably remains constant in the direction of flow. Preferably, the cross-section can also be matched to the cross-section of the filter plate 52 through which the flow passes. This helps to maintain homogeneous pressure conditions even after the flow has passed through the filter plate, which is beneficial for maintaining laminar flow. In principle, however, a different cross-sectional design is also possible from a fluid dynamics perspective. For example, the cross-section can also widen continuously to form an airflow amplifier.

[0082] The effectiveness of the filter assembly 10 can be further improved if the frame 50 is arranged in the housing recess 74 in a substantially airtight or flow-tight manner. This prevents undesirable turbulence in the filter assembly 10.

[0083] According to the invention, the filter device 10 is operated by a method for filtering fibers from a flow, such as an airflow, for a feeding device 20 for feeding the fibers in the production of fiber-reinforced plastics. The feeding device 20 comprises a screw conveyor 30 for laterally feeding fibers into a processing plant 40 for the production of fiber-reinforced plastics. The screw conveyor 30 has a housing 70 with at least one housing bore 76, a screw shaft 80 arranged concentrically in the at least one housing bore 76 and driven about an associated axis of rotation, and a feed opening 72 for feeding the fibers into the at least one housing bore 76.The feed device 20 also includes a suction device for sucking the fibers through the feed opening 72 into the at least one housing bore 76 by means of the flow with a predetermined flow rate, wherein the filter device 10 can be arranged between the suction device and the at least one housing bore 76.

[0084] The filter device 10 comprises at least one filter plate 52, which, in the operating state, can be arranged in a housing recess 74 connected to the at least one housing bore 76 and has a curvature 90 along the at least one housing bore 76 corresponding to its shape. The at least one filter plate 52 has at least one area 64 with several parallel, slit-shaped flow channels 58 extending transversely to the at least one housing bore 76, each with a constant flow cross-section and a predetermined, in particular large, ratio of length l to width b, which generate the effect of several parallel Venturi nozzles, each of which, in the operating state, at the predetermined flow rate in a flow direction 110 and a resulting Reynolds number Re with a value below a predetermined critical range, generates a pressure drop Δp in a predetermined range.This creates laminar flows in the flow channels 58, which generate a homogeneous and uniform pressure distribution in the at least one substantially rectangular area 64 of the at least one filter plate 52.

[0085] The method for operating a filter device 10 advantageously enables secure fixing of the at least one filter plate 52 and yet allows for easy replacement or rotation of the at least one filter plate 52, by the filter device 10 having a frame 50 on which the at least one filter plate 52 is replaceably mounted. The frame 50 has at least one curvature 90 corresponding to the curvature 90 of the at least one filter plate 52, on which the at least one filter plate 52 is mounted.

[0086] The at least one filter plate 52 has leaf spring-like properties and is pre-tensioned with its outer edges 66, which extend along a preferably longer side of the filter plate 52, in grooves 62 of the frame 50 in a form-fitting and / or force-fitting manner, preferably both form-fitting and force-fitting. The at least one filter plate 52 can also be replaced without tools by sliding it in the grooves 62 of the frame 50 by means of another filter plate 52 identical to the at least one filter plate 52, which engages it on a shorter side 68 of the at least one filter plate 52.

[0087] In Fig. Figure 8 illustrates the procedure for replacing or rotating a filter plate 52. The filter plate 52 located in the frame 50 is pushed out of the grooves 62 of the frame 50 to the right, away from the filter plate 52 shown on the left in the image, and can then take its place. The filter plate 52, once removed, can also be rotated 180° around an axis of rotation perpendicular to its surface and reinserted. This effectively extends the service life of the filter plate 52 and reduces costs.

[0088] Fig. Figures 9a to 9c show a sectional view of how, for example, a filter plate 52 can be replaced during operation. This is done as shown in Fig. 9a and Fig. Figure 9b shows the filter assembly 10 being moved downwards into a changeover position within the housing recess 74. The housing 70 serves as an axial detent and thus acts as a locking plate (stop). In the changeover position, according to Fig. 9a to 9c each have a pocket 94 with a radius corresponding to the curvature 90 in the housing 70 as an inlet and outlet for the filter plates 52. In the changeover position, the filter plate 52 can be, as in Fig. 9c is shown, according to the above description Fig. 8, will be replaced. After that, as in Fig. 9b and Fig. 9c shows the filter device 10 in the housing recess 74 being moved back upwards into the working position according to Fig. 9a is moving.

[0089] To remove fiber dust and excessively short fibers, an airflow amplifier can also be provided downstream of the filter unit 10. For this purpose, the air in the housing 70 upstream of the filter unit 10 and / or additional compressed air can be used. If air is supplied through special openings (bores) for compressed air on the underside of the filter unit 10 at a preferably shallow angle, with a cross-section that increases as the opening widens, an increased volume flow is achieved. A compressed air connection can be connected to the bores via distribution lines corresponding to a "multi-jet nozzle". This can also be done in combination with ionized air and can also represent an alternative to an extraction system.

[0090] During the execution of the process, electrostatic charging of the fibers used can be prevented by using an ionized airflow. In particular, this prevents the fibers from adhering to parts of the feeding device, resulting in a more uniform distribution of the fibers during transport and thus also within the plastic of the product being manufactured. Reference symbol list 10 filter system, 20 Feeding device, 30 screw machine, 40 processing plant, Room 49 50 frames, 51 wall, 52 filter plates, 53 Comb, 54 fuse plate, 56 screw, 57 outer edge, 58 Flow channel, 60 central jetty, 62 Nut, 64 area, 66 longer side of the filter plate, 68 shorter side of the filter plate, 70 cases, 72 Feed opening, 74 Housing recess, 76 Housing bore, 80 worm shaft, 90° curvature, 92 Crossbar, 94 bags ( Fig. 9a -9c), 100 fiber shredding device, 110 Flow direction, 120 range of critical Reynolds numbers, 121 critical Reynolds number Re krit , 122 Δp = min., 123 Δp = opt., 124 Δp = max., 125 laminar area, 126 turbulent area, 140 non-movable mold carriers, 150 machine stands, 160 injection molding units, 170 Plasticizing device, 175 plasticizing cylinders, 190 grants. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] EP 2 218 568 A1

[0005] WO 2014 / 048667 A1 [0006, 0007]

Claims

[1] Filter device (10) for filtering fibers from a flow, in particular from an airflow, configured for supplying the fibers in the production of fiber-reinforced plastics, with at least one filter element arranged in and transverse to the flow in a wall (51), characterized by , that at least one filter plate (52) with a curvature (90) is provided as a filter element, which has at least one area (64) with several slit-shaped flow channels (58) which, in the operating state at a predetermined or predeterminable flow rate, has a Reynolds number (Re) with a value below a critical Reynolds number (Re) krit ) exhibit and are thereby designed to form a laminar flow in the flow channels (58) and a homogeneous and uniform pressure distribution in the area (64). [2] Filter device according to claim 1, characterized by, that the filter plate (52) has a closed comb (53) and that the slit-shaped flow channels (58) are several parallel slit-shaped flow channels (58) each with a constant flow cross-section and a predetermined ratio of length (l) to width (b). [3] Filter device according to claim 1 or 2, characterized by , that the wall (51) is a cylindrical wall of a housing bore (76) with an inner radius for receiving a conveying means with a cylindrical cross-section, such as a screw shaft (80) of a feeding device (20) for feeding the fibers into a processing plant (40) and is designed to be preferably swept over by the conveying means arranged in the at least one housing bore (76) during the removal of the filtered fibers without contact, and that the filter element is pre-curved and has a curvature (90) corresponding to the shape of the housing bore (76). [4] Filter device according to any one of the preceding claims, characterized by , that the radius of the curvature (90) of the filter plate (52) in the uninstalled state is larger than the inner radius of the wall (51). [5] Filter device (10) according to any one of the preceding claims, characterized by , that the filter device (10) has a frame (50) or a receptacle which has at least one curvature (90) corresponding to the curvature (90) of the wall (51), on which the at least one filter plate (52) is replaceably mounted, wherein in the operating state the frame is preferably arranged in a housing recess (74) connected to the at least one housing bore (76). [6] Filter device (10) according to claim 5, characterized by, that the at least one filter plate (52) has leaf spring-like properties and is pre-tensioned with its outer edges (57), which run along a preferably longer side (66) of the filter plate (52), being received in grooves (62) of the frame in a form-fitting and / or force-fitting manner. [7] Filter device (10) according to claim 5 or 6, characterized by, that the filter device (10) has several filter plates (52) arranged side by side with bulges (90) which are mounted on several corresponding bulges (90) of the frame and which, in the operating state when using a multi-shaft screw machine (30), can be arranged with several adjacent interpenetrating housing bores (76) with a screw shaft (80) arranged therein, and that the frame (50) has at least one central web (60) with grooves (62) between the filter plates (52) which are designed to receive outer edges (57) of the filter plates (52) in a form-fitting and / or force-fitting manner. [8] Filter device (10) according to one of claims 5 to 7, characterized by, that the at least one filter plate (52) has symmetrical properties and is therefore designed to allow installation in the frame (50) rotated by 180°, and that the frame (50) and the at least one filter plate (52) are designed to allow replacement or rotation of the at least one filter plate (52) by means of a sliding removal mechanism. [9] Filter device (10) according to any one of claims 5 to 8, characterized by , that the filter device (10) has symmetrical properties and is therefore designed to be installed rotated by 180° into the housing recess (74). [10] Filter device (10) according to one of claims 5 to 9, characterized by , that the at least one filter plate (52) on the frame (50) is secured against displacement in the grooves (62) by two locking plates (54) which are arranged at the front of the frame (50) and are detachably attached to it. [11] Filter device (10) according to any of the preceding claims, characterized by , that the at least one filter plate (52) has several substantially rectangular, separated areas (64) arranged along a preferably longer side of the filter plate (52) with several slit-shaped flow channels (58). [12] Filter device (10) according to one of the preceding claims, characterized by , that the flow channels (58) are designed to generate a pressure drop (Δp) in a range around 50 mbar. [13] Filter device (10) according to any of the preceding claims, characterized by , that at least one filter plate (52) has a thickness between 0.5 mm and 2 mm. [14] Filter device (10) according to any one of claims 5 to 13, characterized by, that the frame (50) has at least one space (49) with a cross-section that remains constant in the direction of flow downstream of the filter plate (52) and following the filter plate. [15] Filter device (10) according to any one of claims 5 to 14, characterized by , that the frame (50) is arranged in the housing recess (74) in a substantially airtight or flow-tight manner. [16] Feeding device (20) for feeding fibers in the production of fiber-reinforced plastics, comprising at least one screw machine (30) for feeding fibers into a processing plant (40) with a housing (70) having at least one housing bore (76), a screw shaft (80) arranged concentrically in the at least one housing bore (76) and driven about an associated axis of rotation, and a feed opening (72) for feeding the fibers into the at least one housing bore (76), wherein the feeding device (20) has a suction device for drawing the fibers through the feed opening (72) into the at least one housing bore (76) by means of a flow, in particular an airflow, with a predetermined flow rate, and with a filter device (10) arranged between the suction device and the at least one housing bore (76) for filtering the fibers out of the flow, characterized bya filter device (10) according to one of the preceding claims. [17] Method for operating a filter device (10) for filtering fibers from a flow, in particular from an air flow, for supplying the fibers in the production of fiber-reinforced plastics, with at least one filter element arranged in and transverse to the flow in a wall (51), characterized by , that at least one filter plate (52) with a curvature (90) is used as a filter element, which has at least one area (64) with several slit-shaped flow channels (58) which, in the operating state at a predetermined or predeterminable flow rate, has a Reynolds number (Re) with a value below a critical Reynolds number (Re) krit ) generate a laminar flow in the flow channels (58) and a homogeneous and uniform pressure distribution in the area (64). [18] Method according to claim 17, characterized by, that the flow channels (58) generate a pressure drop (Δp) in a range around 50 mbar. [19] Method according to claim 17 or 18, characterized by , that the at least one filter plate (52) is mounted interchangeably on a curvature of a frame (50), wherein the curvature of the frame corresponds approximately to the curvature (90) of the at least one filter plate (52), and that the at least one filter plate (52) is received in a leaf spring-like and pre-tensioned manner with its outer edges (66) in grooves (62) of the frame (50) in a form-fitting and / or force-fitting manner, and that the at least one filter plate (52) can be replaced without tools by sliding it in the grooves (62) by means of another filter plate (52) identical to the at least one filter plate (52), which engages on one side (68) of the at least one filter plate (52). [20] Method according to any one of claims 17 to 19, characterized by , that an ionized airflow is used as the flow.

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